Jerk and stall when put into gear?

When it does move, you have constant backfires and no power? You sure Timing is correct. Verify 8-10 BTDC as starting point.

Here's my thought

Verify Firing order set correctly on the distributor to the head. These engines run can run/idle on just 3 cylindars. If one pair of plug wires is crossed, it could be, you might not necessarily see it at idle.

If Points, Verify Dwell is set correctly.

Then I'd start looking for intake leaks. Carburator Base Gasket leak? Intake Vacuum Leak? Intake Gasket Leak?